Chlorination of electrolytic copper refinery slimes in a molten salt bath



United States, Patent CHLORINATIGN 0F ELECTROLYTIC COPPER REFINERYSLIMES IN A MOLTEN SALT BATH Svante Mellgren, Metuchen, William R. Opie,Keyport,

and Lamar D. Catlin, Edison, N.J., assignors to American Metal Climax,Inc., New York, N.Y., a corporation of New York No Drawing. Filed May 5,1964, Ser. No. 365,164 9 Claims. (Cl. 23-98) The present invention isdirected to a process for treating electrolytic copper refinery slimes.

Almost all selenium and tellurium are obtained as a by-product ofprecious metals recovery from electrolytic copper refinery slimes, oftenalso called anode mud, electrolytic residues, and sludges, which are allmeant to be included in the term slimes as used herein. Slimes usuallycontain gold, silver, platinum group metals, copper, lead, tin,antimony, selenium, tellurium, arsenic, etc., and minor amounts of allother metals dependent upon the source.

It is an object of the present invention to provide an economicalprocess for treating slimes. It is also an object of the presentinvention to provide a process for recovering selenium and telluriumfrom slimes. Other objects and advantages of this invention will becomeapparent from the specification.

The present invention contemplates the chlorination of slimes in amolten salt environment at elevated temperatures to convert selenium andtellurium found in the slimes to the respective chlorides and recoveringsaid chlorides as volatile products.

Slimes, as collected periodically from the copper refinery tanks, areusually screened to remove large particles of metallic copper. They arethen usually decopperized as, for example, by subjecting the material to'an acid leach preliminary to further treatment. In accordance with thepresent invention, the decopperized slimes are added to a molten saltbath and treated with gaseous chlorine, to form the chlorides ofselenium and tellurium.

The slimes are added to the bath when it is molten or mixed with thesalts before they are heated. The bath is preferably agitated to obtaingood distribution of slimes and gas. The bath may be mechanicallyagitated, e.g. by an impeller. The slimes are believed to be in aphysical state of suspension in the molten salt bath. Relatively largeamounts of slimes may be added to the bath, e.g. 500 grams of slime per1700 grams of molten salt in the bath. Although low concentrations ofslimes in the bath may be used, it is not an economical utilization ofequipment. As the slime concentration in the bath is raised to very highconcentrations, the viscosity of the resultant bath is increased. Themaximum practicable concentration of slimes in a given bath is that atwhich the viscosity is increased to the point where effective agitationis difiicult and the resultant distribution of chlorine gas in the meltbecomes uneven. Suitable baths include the alkali metal halides and thealkaline earth metal halides with the chlorides being preferred. Theseare sodium chloride, potassium chloride, lithium chloride, rubidiumchloride, cesium chloride, magnesium chloride, calcium chloride,strontium chloride, and barium chloride. Generally those electrolyteshaving lower melting points are preferred. The low melting mixtures ofpotassium chloride and sodium chloride are preferred because of theirexcellent bat-h properties and low cost. The preferred baths are thosein which chlorine is at least somewhat soluble.

The chlorination process may be carried out at all tem- "ice peraturesat which the electrolyte is molten. It is generally preferred that thetemperature should not be higher than about 900 C. to prevent vaporlosses when low melting salts, e.g., the eutectic mixture of sodium andpotassium chloride with a melting point of about 650- 675 C., are used.These vapor losses are undesirable in two respects: The obvious loss ofbath salts which must be replaced, and the contamination of the volatilechloride products from which they must be separated. Although it ispreferred that the chlorination reaction be carried out between about750 and 900 C., the reaction may be carried out at temperatures as lowas about 350 C. Baths having relatively low melting points may beobtained by incorporating one or more additional components such asaluminum chloride and the like into the system to effect depression ofthe melting point. Depression of the melting point of the bath islikewise effected by the accumulation in the bath of soluble chloridesalts e.g. of lead, silver etc. during the chlorina tion reaction.

Although the process may be carried out in a continuous manner, thecontemplated commercial process based upon the quantity of slimesavailable for treatment indicates that a batch process should be mosteconomical. After the addition of the slimes to the molten saltelectrolyte, chlorine gas is passed through the electrolyte. It ispreferably inserted at or near the lower portions of the chamber holdingthe bath. The total chlorine required varies with the amount of metalvalue in the slimes susceptible to chlorination. Generally, the use ofbetween about 0.3 pound of chlorine to about 0.7 pound of chlorine perpound of slimes is satisfactory. It is preferred to utilize sufficientchlorine so that the higher chlorides of the metals are formed and gooff in the form of the volatile reaction products.

In the treatment of slimes from certain sources it may be useful toemploy a reducing agent during the chlorination process. This may beaccomplished by the addition of finely subdivided carbon, e.g. cokebreeze, with the slimes in the charge to the reaction chamber. It ismore conveniently accomplished by passing carbon monoxide through thereaction chamber simultaneously with the introductionof chlorine gas tothe reaction chamber.

The reaction chamber is formed from refractory materials, e.g. quartz,and the acid or basic refractories. The cell is closed with exit portsabove the molten bath through which the volatile reaction products arewithdrawn.

Slimes often also contain antimony, arsenic and tin. When slimescontaining such metals are treated by the instant process, these metalsare largely eliminated from the bath through formation of their volatilechlorides.

The invention is illustrated in the examples but is not to 'be construedas limited to the details described therein. The parts and percentagesare by weight except where specifically indicated otherwise.

1700 gms. of a mixture of potassium chloride and sodium chloride (theeutectic mixture having a 1:1 molar ratio) was melted in a quartzcylinder 7% inches high and 5 inches in diameter. The heat was appliedexternally. The temperature of the bath was brought to 750 C. andmaintained there. 500 gms. of slimes containing selenium, tellurium,antimony, arsenic, tin, lead and precious metals were added to the bath.The bath Was agitated by rotation of a quartz impeller at the end of aquartz rod which was suspended above the bath. After the addition of theslimes, the bath was still very fluid. Chlorine gas was passed throughthe bath by means of an input tube which extended through the topsurface of the bath almost to the bottom of the crucible. The chlorinegas was added over a period of 2% hours. The

' A similar test was run following the procedure described in thepreceding paragraph with the exception that carbon monoxide was addedwith the chlorine; the proportion of chlorine to carbon monoxide being5:1 by volume. Similar results were obtained.

Similar results are obtained using other baths and differentconcentrations of slimes in the bath. Longer reaction time and somewhathigher temperautres, e.g. 900? 0, result in the obtention of betteryields of the desired chlorides.

The volatile chloride products produced during the chlorination arevented from the closed space above the molten bath to and through anaqueous scrubber. A portion of the selenium chloride and the telluriumchloride dissolves in the aqueous solution with the remainderprecipitating in the scrubber. Most of the antimony chloride and arsenicchloride go into solution in the scrubber. Successful recovery has beenobtained utilizing water, alkaline solutions (e.g. 30% NaOH) andalsoacid solutions (e.g. 6 N HCl and 20% H 80 in the scrubber. The preferredrecovery system consists of passing the volatile products through twowater scrubbers in series followed by final cleaning in a sodiumhydroxide solution. The volatile chlorides may be separated andrecovered after removal from the scrubbing system by separatorytechniques, e.g. precipitating the selenium and tellurium separatelyfrom a hydrochloric acid solution with additions of S0 washed and thewashed solution is combined with the hydrochloric acid solution.

The residual slimes from the chlorination'reaction may be separated fromthe salt bath by dissolving the salts away in aqueous solution. Theresidue may then be dechlorinated and treated to recover the remainingmetal values which include the precious metals.

The process described herein is relatively simple and economical. Theprocess also yields a slime residue containing the precious metals whichis susceptible to treatment by a novel and economical process.

Obviously, many modifications and variations of the invention arepossible in the light of the above teachings.

It is therefore to be understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed.

What is claimed is:

1. A process for simultaneously separating selenium and telluriumtogether with any antimony, arsenic and tin values present inelectrolytic copper refinery slimes from other metal values contained insaid slimes the chlorides of which are relatively non-volatile attemperatures of up to 900 C. compared to the chorides of selenium,tellurium, antimony, arsenic and tin, said proc- The precipitatedmaterial is.

ess comprising the steps of providing a molten salt bath consistingessentially of at least one salt selected fromthe group consisting ofalkali metal halides, alkaline earth metal halides, and mixtures thereofand containing said electrolytic copper refinery slimes, passing gaseouschlorine through the molten bath while maintaining said bath at atemperature of from 350 to 900 C. whereby the selenium, tellurium,antimony, arsenic and tin values are converted to volatile chlorides andcollectively separating said volatile chorides from the nonvolatilesubstances.

2. The process of claim 1 wherein aluminum chloride is additionallyincluded in the salt bath to lower the melting point thereof.

3. The process of claim 1 wherein the alkali metal halides and alkalineearth halides are chlorides.

4. The process of claim 1 wherein the bath is agitated during thepassage of chlorine therethrough.

5. The process of claim 4 wherein the total amount of chlorine passedthrough the bath is between 0.3 and 0.7 pound per pound of electrolyticcopper refinery slimes in the bath.

6. The process of claim 1 wherein the salt bath consists essentially ofthe eutectic mixture of potassium chloride and sodium chloride.

7. The process of claim 1 wherein a reducing agent is additionallyincluded in the molten salt bath when passing chlorine therethrough.

8. The process of claim 1 wherein the electrolytic copper refineryslimes are decopperized prior to use in the molten salt bath.

9. A process for simultaneously separating selenium and telluriumtogether with any antimony, arsenic and tin values present inelectrolytic copper refinery slimes from other metal values contained insaid slimes the chlorides of which are relatively non-volatile attemperatures of up to 900 C. compared to the chlorides of selenium,tellurium, antimony, arsenic and tin, said process comprising the stepsof providing a molten salt bath consisting essentially of at least onesalt selected from the .group consisting of alkali metal halides,alkaline earth metal halides and mixtures thereof and containing saidelectrolytic copper refinery slimes, passing gaseous chlorine and carbonmonoxide gas concomitantly through the molten bath while maintainingsaid 'bath at a temperature of from 350 to 900 C. and collectivelyseparating the resulting volatile chlorides from the non-volatilesubstances.

References Cited by the Examiner UNITED STATES PATENTS 845,868 3/1907Fronek 23--1 890,432 6/1908 Masson 2398 X 1,931,944 10/1933 Wood et al23--98 OTHER REFERENCES I Ser..No. 292,742, Beck et al. (A.P.C.),published July 1943.

MILTQN WEISSMAN, Primary Examiner.

EDWARD STERN, Examiner.

1. A PROCESS FOR SIMULTANEOUSLY SEPARATING SELENIUM AND TELLURIUMTOGETHER WITH ANY ANTIMONY, ARSENIC AND TIN VALUES PRESENT INELECTROLYTIC COPPER REFINERYY SLIMES FROM OTHER METAL VALUES CONTAINEDIN SAID SLIMES THE CHLORIDES OF WHICH ARE RELATIVELY NON-VOLATILE ATTEMPERATURES OF UP TO 900*C. COMPARED TO THE CHLORIDES OF SELENIU,TELLURIUM, ANTIMONY, ARSENIC AND TIN, SAID PROCESS COMPRISING THE STEPSOF PROVIDING A MOLTEN SALT BATH CONSISTING ESSENTIALLY OF AT LEAST ONESALT SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL HALIDES,ALKALINE EARTHP METAL HALIDES AND MIXTURES THEREOF AND CONTAINING SAIDELECTROLYTIC COPPER REFINERY SLIMES, PASSING GASEOUS CHLORINE THROUGHTHE MOLTEN BATH WHILE MAINTAINING SAID BATH AT A TEMPERATURE OF FROM 350TO 900*C. WHEREBY THE SELENIU, TELLURIUM, ANTIMONY, ARSENIC AND TINVALUES ARE CONVERTED TO VOLATILE CHLORIDES AND COLLECTIVELY SEPARATINGSAID VOLATILE CHLORIDES FROM THE NONVOLATILE SUBSTANCES.